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New Scientist Live

Milky Way’s core could be spewing out planet-sized star chunks

A black hole’s spitball may be in our vicinity

Mark A. Garlick

By Leah Crane

The Milky Way’s supermassive black hole could be chewing up stars and spitting chunks back out at us. If so, planet-sized bits of stars may be shooting away from black holes and hurtling across the universe at incredible speeds, according to results presented at the meeting of the American Astronomical Society in Grapevine, Texas, this week.

That stretched-out matter does not end up exactly uniform, so clumps the size of planets coalesce under their own gravity. Those “planets”, with masses ranging from around that of Neptune to several times that of Jupiter, are then flung away from the central black hole at speeds up to 10,000 kilometres per second, simulations by James Guillochon at the Harvard-Smithsonian Center for Astrophysics and Eden Girma at Harvard College suggest.

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This should happen relatively often – by their calculations, one out of every thousand free-floating planet-sized bodies should be formed in this way. The closest one to Earth could be a few hundred light years away, and could have arrived from 50 million light years away.

Transporting worlds

“Usually, from something that far away, we’re only getting light or maybe high-energy particles,” says Guillochon. “This is a way to transport entire worlds from one corner of the universe to the other.”

These chunks of spaghettified stars will have a distinctive composition: each one will be a sample of a different part of its parent star. It’s like dicing a tomato, says Guillochon – some chunks will be all peel and some will be all seeds.

Such objects are nearly impossible to detect visually because of their faintness and speed, and no one has seen one so far. We could hunt them down based on how their gravity bends the light of stars behind them, but it will be years before that is possible. Plus, there are several other ways to accelerate similar objects to high speeds, says Avi Loeb, also at the Harvard-Smithsonian Center for Astrophysics although not involved in this research.

But, Loeb says, this is still exciting work. “It provides us with the possibility of detecting a whole new population of objects that were otherwise unexpected.”